Apparatus and method for frequency conversion

ABSTRACT

An apparatus for frequency up conversion and down conversion using frequency multiplier circuits. The frequency multiplier circuits receive a lower frequency signal and are operated in a forward direction to provide a higher frequency output. The same frequency multiplier circuits are operated in a reverse direction by receiving a higher frequency signal and producing a lower frequency output. The frequency multiplier circuits preferably use heterojunction barrier varactor diodes to eliminate the need for DC bias or idler circuitry.

BACKGROUND

1. Field

The present invention relates to translating lower frequency signals tohigher frequency signals and higher frequency signals to lower frequencysignals. More specifically, the present invention relates to anapparatus and method for up converting microwave signals to millimeterwave signals and down converting millimeter wave signals to microwavesignals for use in such applications as a radar transceiver.

2. Description of Related Art

Communication and radar systems operating with signals in the microwavefrequency band (3–30 GHz) are well-known in the art. Systems operatingat higher frequencies are also known in the art. Such systems are oftenimplemented using one or more transceivers that both transmit andreceive the signals. Operating at higher frequencies is desirablebecause the size of the antennas used with the transceiver scaleinversely with the operational frequency. As a result, higherfrequencies result in smaller antennas while still realizing the samegain. This is important for applications that require a compacttransceiver, such as in commercial vehicular applications. Higherfrequencies also provide better Doppler resolution thus improving thequality of data transmitted and received.

Millimeter wave transceivers are typically designed with frequencymultiplier stages immediately following the voltage controlledoscillator (VCO). As a result, all the components of the transceiver(mixers, amplifiers, etc.) must be operable at the higher multipliedfrequency which increases the cost of the components. Furthermore,typical frequency multiplier stages comprise expensive active componentsthat require complicated circuitry and introduce undesirable noise intothe system.

FIG. 1 shows a prior art automobile radar system 200 for operationwithin the millimeter wave frequency band. The system 200 comprises anoscillator 210 operating at 19–19.25 GHz followed by a first amplifier212. The amplified signal is then doubled in frequency by a firstfrequency multiplier 220. The doubled frequency signal is then amplifiedby a second amplifier 222. A second multiplier 230 then doubles thefrequency of the signal to be at 76–77 GHz. A Microwave MonolithicIntegrated Circuit (MMIC) switch 240 is then used to switch the signalamong multiple antenna elements 250 for transmission. A radar returnsignal is received by the antenna elements 250 and is directed to amixer 260 by the MMIC switch 240. Since the transmitted signal is at76–77 GHz, the mixer 260 uses a Local Oscillator signal at the samefrequency to downconvert the radar return signal to an IntermediateFrequency (IF) signal. A low pass filter 262 is used to filter outsignals at frequencies higher than that of the IF signal.

The system depicted in FIG. 1 illustrates some of the problems seen withtransceiver systems known in the art. As can be seen from FIG. 1,multiple frequency multiplier stages are used after the voltagecontrolled oscillator to translate the oscillator signal at a microwavefrequency to a signal in the millimeter wave frequency band. Thesecomponents can impose considerable cost, size and power constraints onthe system compared to components that need only operate at lowerfrequencies. Further, down conversion of the radar return is achievedwith a mixer operating in the millimeter wave frequency band. Again,such components operating in the millimeter wave frequency band may costconsiderably more, be larger than, and/or require more power thancomponents that need only operate at lower frequencies.

Therefore, there is a need for an apparatus and method for sending andreceiving signals at higher frequencies that can utilize components forlower frequency applications, while still providing the benefits ofoperation at higher frequencies.

SUMMARY

Frequency multipliers provide the ability to convert a signal at a firstfrequency to a signal at a second, higher, frequency. Similarly,frequency dividers provide the ability to convert a signal at a firstfrequency to a signal at a second, lower, frequency. According toembodiments of the present invention, a passive frequency multiplier isoperated in a forward direction to produce an output signal that is at afrequency that is a multiple of the frequency of the input signal. Thepassive frequency multiplier is also operated in a reverse direction toproduce an output signal that is at a frequency that is a fraction ofthe frequency of the input signal. Operation of a frequency tripler isdescribed, but the passive frequency multiplier according to embodimentsof the present invention may provide other harmonics of an input signal.

Embodiments of the present invention provide an apparatus for frequencyup conversion and down conversion using frequency multiplier circuits.The frequency multiplier circuits receive a lower frequency signal andare operated in a forward direction to provide a higher frequencyoutput. The same frequency multiplier circuits are operated in a reversedirection by receiving a higher frequency signal and producing a lowerfrequency output.

Transceivers according to embodiments of the present invention allow forthe same circuitry to be used for both frequency up conversion and downconversion, resulting in significant savings in cost, complexity, size,weight, and other factors as compared to other transceivers known in theart. For example, a transceiver according to an embodiment of thepresent invention may use a passive frequency multiplier comprising avaractor diode. In the transceiver, the varactor diode, in combinationwith passive components, is disposed to provide for up conversion of atransmitted signal and down conversion of a received signal. A preferredembodiment of the present invention uses a heterojunction barriervaractor (HBV) diode in the passive frequency multiplier. Due to the useof the HBV diode, no DC bias or idler circuitry is required for themultiplier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (prior art) shows a simplified block diagram of an automobileradar system.

FIG. 2 shows the small signal C-V and I-V characteristics of aheterojunction barrier varactor.

FIG. 3 shows a schematic of a HBV-based circuit that may be used as botha frequency multiplier and a frequency divider.

FIG. 4 shows a schematic of another HBV-based circuit that may be usedas both a frequency multiplier and a frequency divider.

FIG. 5 shows a transceiver according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Further, the dimensions of certainelements shown in the accompanying drawings may be exaggerated to moreclearly show details. The present invention should not be construed asbeing limited to the dimensional relations shown in the drawings, norshould the individual elements shown in the drawings be construed to belimited to the dimensions shown.

As shown in FIG. 1, up conversion from a microwave frequency signal to amillimeter wave frequency signal may be accomplished by using a seriesof frequency doublers. Up conversion from a microwave frequency signal(or from a lower frequency millimeter wave signal) to a higher frequencymillimeter wave signal may also be accomplished by using one or morecircuits that provide multiples of odd harmonics of a signal, e.g.,frequency triplers. Frequency triplers may be realized using severaldifferent techniques, such as, for example, a Schottky diode triplercircuit.

Passive frequency multipliers according to embodiments of the presentinvention may also be configured so as to provide for frequencydivision. That is, rather than up converting an input signal to anoutput having a frequency that is a multiple of the input frequency, thecircuit may be configured to provide an output that has a frequency thatis a divisor of the input frequency, i.e., providing an output that isat a subharmonic of the input frequency. Further, as described below, apassive frequency multiplier may be configured in a bi-directionalfashion to provide for frequency multiplication in one direction andfrequency division in the opposite direction.

Frequency multipliers according to embodiments of the present invention,such as frequency triplers, may be realized by using a heterojunctionbarrier varactor (HBV) diode. HBV diodes have a symmetric Capacitance(C) versus Voltage (V) characteristic and an anti-symmetric Current (I)versus Voltage (V) characteristic, although an HBV diode typically drawsno appreciable current over the operating range of interest. FIG. 2illustrates the C-V characteristic 53 and the I-V characteristic 57 fora typical HBV diode. HBV diodes are typically extremely small (tens ofmicrons) and are easy to fabricate with very high yields. These diodescan be implemented using common semiconductor fabrication processes andtypical semiconductor materials, such as Indium Phosphide (InP) orGallium Arsenide (GaAs). See, for example, Saglam et al., “450 GHzmm-wave signal from a frequency tripler with heterostructure barriervaractors on gold substrate,” ELECTRONICS LETTERS, 20 Jul. 2002, vol.38, no. 13, pp. 657–658.

An advantage of HBV diode-based frequency multipliers is that no DC biascircuitry is required. A further advantage is that no idler circuitry isrequired for the even harmonics. These advantages provide that thecircuitry in an HBV diode-based frequency multiplier may be simpler thanother diode-based frequency multipliers, such as Schottky diode-basedfrequency triplers.

FIG. 3 presents a schematic diagram of an HBV diode-based frequencymultiplier circuit 300 using lumped elements according to an embodimentof the present invention. Preferably, the circuit 300 presents animpedance match at both its input and its output. The impedance of thesource is represented by a source impedance 311 having a value of Zo andthe impedance at the output is represented by an output impedance 321having a value of Zo. Using lumped elements, the inductances at theinput and output of the multiplier circuit 300 are represented by lumpedsource inductance 313 having a value of Ls and a lumped output impedance323 having a value of Lo.

As shown in FIG. 3, the HBV diode 330 requires no diode bias, so theterminals of the HBV diode 330 are connected in series with the sourceimpedance 311 and the output impedance 321. For operation as a frequencytripler, the shunt LC network 340 at the input is configured to presentan open circuit at the fundamental frequency f₀ and a short circuit atthe triple frequency 3f₀. Similarly, the shunt LC network 350 at theoutput is configured to present a short circuit at the fundamentalfrequency f₀ and an open circuit at the triple frequency 3f₀. As shownin FIG. 3, the input shunt LC network 340 comprises an inductance 341having a value of La1 in series with a first tank circuit 345 having aninductor 346 with value La2 in parallel with a capacitor 348 with valueCa. The output shunt LC network 350 comprises a capacitor 351 having avalue of Cb1 in series with a second tank circuit 355 having an inductor356 with value La in parallel with a capacitor 358 with value Cb2.However, those skilled in the art will understand that the input shuntLC network 340 and the output shunt LC network 350 may be realized usingother configurations or distributions of elements.

The HBV diode-based tripler circuits are typically used just for thatcapability, that is, to provide an output signal which is triple thefrequency of an input signal. However, the HBV tripler circuit shown inFIG. 3 may also be operated in reverse. When operated in the reversemanner, a signal inserted at the “output” end of the circuit having afrequency of 3f₀ will result in a signal being output at the “input” endof the circuit with a frequency of f₀. Therefore, a frequency multipliercircuit according to an embodiment of the present invention using an HBVdiode also provides the capability of being a frequency divider circuit.

By choosing the element values of the shunt networks 340, 350 in FIG. 3correctly, one can achieve input and output impedance matches andmaximize the conversion efficiency for a given diode characteristic.Simulations indicate that for a typical HBV diode characteristic, suchas C_(max)/C_(min) ratio of 5 and a series resistance of 5 Ohms, the upconversion (multiplier by 3) efficiency is 84% and the down conversion(divider by 3) efficiency is 55%. Those skilled in the art willunderstand that operating a fabricated circuit at millimeter wavefrequencies will result in loss mechanisms not included in the idealizedanalysis discussed above. Therefore, actual efficiencies will probablybe much less. However, these idealized efficiencies and the relatedanalysis demonstrate the applicability of HBV diode-based triplercircuits for both up conversion and down conversion.

Through the choice of the element values for the shunt networks 340, 350of the circuit shown in FIG. 3, the circuit may also be configured tooperate as a 5 times multiplier and a ⅕ divider. That is, by choosingthe element values such that the shunt LC network 340 at the input isconfigured to present an open circuit at the fundamental frequency f₀and a short circuit at the frequency 5f₀ and the shunt LC network 350 atthe output is configured to present a short circuit at the fundamentalfrequency f₀ and an open circuit at the frequency 5f₀, the circuitfunctions as a 5× multiplier and divider. However, the efficiency of thecircuit will be less than that seen in the triple configuration. Theoperation of the circuit depicted in FIG. 3 may also be extended toother odd harmonics of the fundamental frequency through the properchoice of element values, but also with decreases in efficiency.

FIG. 4 shows a schematic of another HBV diode-based frequencymultiplier/divider circuit 400. In FIG. 4, the HBV diode 430 is disposedas a shunt diode where the common terminal to a first series LC network440 and a second series LC network 450. For operation as a frequencytripler, the first series LC network 440 is configured to present ashort circuit at the fundamental frequency f₀ and an open circuit at thetriple frequency 3f₀ and the second series LC network 450 is configuredto present an open circuit at the fundamental frequency f₀ and a shortcircuit at the triple frequency 3f₀. Hence, a signal from Vin at thefundamental frequency f₀ will reach the HBV diode 430 for the generationof odd harmonics of the signal, but the signal at the fundamentalfrequency f₀ will be blocked from reaching Vout. Similarly, a signal atthe triple frequency 3f₀ presented at Vout will reach the HBV diode forthe generation of odd subharmonics, but the signal at the triplefrequency 3f₀ will be blocked from reaching Vin. Hence, the circuit 400provides for frequency multiplication by three in one direction andfrequency division by three in the other direction.

An embodiment of the present invention provides an apparatus used forthe transmission and reception of electro-magnetic signals. Preferably,the apparatus is operated to radiate and receive signals in themillimeter wave band. Shown in FIG. 5 is a schematic diagram of anapparatus that may be used in accordance with the present invention. Theapparatus comprises a transceiver unit 100, two 180 degree couplers 152,154, two frequency multiplier circuits 122, 124, a transmit antenna 132,and a receive antenna 134. The 180 degree couplers 152, 154 arepreferably 180 degree hybrid couplers.

As discussed above, transceiver units in general are well-known.Therefore, the transceiver unit 100 may comprise a unit that isavailable as a commercial-off-the-shelf (COTS) unit. The transceiverunit 100 comprises a voltage-controlled oscillator (VCO) 102 thatprovides a modulated carrier signal at a selected frequency. Forexemplary purposes only, the discussion below will refer to a 50 GHztransceiver, in other words, the VCO modulates the baseband signal ontoa 50 GHz carrier signal. Those skilled in the art will realize thatVCO's generating other frequencies are readily available and can be usedwith this invention.

The modulated signal may provide both the transmit signal from thetransceiver unit 100 and a local oscillator signal used for internaldown conversion of a received signal. The modulated signal is receivedby a coupler 104 that splits the signal into two outputs. The firstoutput is coupled to the transmit port 106 of the transceiver unit 100and the second output, acting as a local oscillator signal, is coupledto an internal mixer 112 of the transceiver unit 100. The internal mixermixes the local oscillator signal with a signal received from thereceive port of the transceiver unit 100 to produce a baseband signal.The baseband signal can then be converted to a digital signal by theanalog-to-digital converter 114.

Those skilled in the art understand that the description of thetransceiver unit 100 presented above describes a relatively simpletransceiver unit 100. Other transceiver units known in the art maycomprise other features, elements, and/or functions. However, such unitsmay be generally characterized as modulating a baseband signal andproducing a modulated transmit signal at a transmit port and receiving amodulated receive signal at a receive port and producing a demodulatedbaseband signal.

The transmit signal at the fundamental frequency f₀ exits thetransceiver unit 100 via transmit port 106 where it is received by thefirst 180 degree coupler 152. The 180 degree coupler 152 is a four portbi-directional asymmetric coupling device that has the followingscattering matrix [S]:

$\lbrack S\rbrack = {\frac{1}{\sqrt{2}}\left\lbrack \begin{matrix}0 & 1 & 1 & 0 \\1 & 0 & 0 & {- 1} \\1 & 0 & 0 & 1 \\0 & {- 1} & 1 & 0\end{matrix} \right\rbrack}$Hence, the 180 degree coupler has a 180° difference at ports B and Cwhen fed at port D and no phase difference between ports B and C whenfed at port A. Therefore, the application of a transmit signal at port Aof the first 180 degree coupler 152 will result in signals at ports Band C at the fundamental frequency f₀ having equal amplitude and equalphase, while there will be no output at port D. Preferably, the first180 degree coupler 152 is chosen or configured for operation at andaround the fundamental frequency f₀.

The two signals from the first 180 degree coupler are each coupled to aseparate frequency multiplier circuits 122, 124 to provide for upconversion of the fundamental frequency f₀ to a multiple of thefundamental frequency, in this case, 3f₀. The frequency multipliercircuits 122, 124 preferably comprise passive diode-based frequencymultiplier circuits. More specifically, the passive diode-basedfrequency multiplier circuits 122, 124 preferably each comprise a HBVtripler circuit as described above. The HBV tripler circuit is preferredbecause it uses passive elements, which help reduce noise and itrequires no DC bias source, thus maintaining circuit simplicity.

The outputs of the frequency multiplier circuits 122, 124 are coupled tothe second 180 degree coupler 154. The second 180 degree coupler 154 issimilar to the first coupler 152 in that it is also a four portbi-directional coupler having the scattering matrix described above.Preferably, the second 180 degree coupler 152 is chosen or configuredfor operation at and around the multiplied frequency 3f₀. Due to theoperation of the second 180 degree coupler 154, the outputs of thefrequency multiplier circuits are added together at the coupler portconnected to the transmit antenna 132 and are subtracted from each otherat the port connected to the receive antenna 134. Thus, the transmitantenna 132 transmits a signal at the desired multiple of thefundamental frequency and no signal is output by the receive antenna134. Therefore, if the frequency multiplier circuits 122, 124 areconfigured as tripler circuits, a 50 GHz carrier signal from thetransceiver 100 will be output as a 150 GHz radiated signal.

Similarly, the receive antenna 134 may be configured to receive signalsat the desired multiple of the fundamental frequency. The signalreceived by the receive antenna 134 is directed to the second 180 degreecoupler 154, which splits the received signal into two signals at portsA and D that have an equal or nearly equal amplitude, but are 180degrees out of phase with each other. These signals are then coupled tothe frequency multiplier circuits 122, 124, which, due to theirbi-directional capability, provide for down conversion of the receivedsignals to the fundamental frequency. The down converted outputs of thefrequency multiplier circuits 122, 124 are then directed to the first180 degree coupler 152. The first 180 degree coupler 152 provides thatthe down converted received signals will be added and output by thecoupler 152 at port D, while any signals received by the transmitantenna 132 flowing back through the system will be subtracted from eachother and not output at port D of coupler 152.

The down-converted received signal from the first coupler 152 enters thetransceiver 100 through the receive port 108. The use of a HBVdiode-based frequency multiplier circuit may introduce insertion loss,which may decrease the sensitivity of the transceiver 100. To alleviatethis problem, a low noise amplifier (LNA) 110 may be used to amplify thereceived signal output from the first coupler 152. Of course, the use ofa LNA operating at high frequencies may increase the cost, size, and/orpower requirements of the circuit or result in other limitations. As analternative, no amplifier may be used and the reduced sensitivity isaccepted as a tradeoff for reduced costs. As discussed above, thetransceiver 100 mixes the down-converted received signal with the localoscillator signal to produce a baseband signal.

The embodiment of the present invention described above presents atransceiver, which may normally operate at a frequency of 50 GHz, thatcan be reconfigured to operate at 150 GHz through the use of relativelylow cost diode-based frequency multiplier circuits. As described above,HBV diode-based frequency multiplier circuits can be configured tooperate as frequency triplers or as other odd harmonic multipliers anddividers, providing for transceiver operation at even higherfrequencies.

Although the transceiver 100 has been described above in terms ofincorporating the frequency multiplier circuits depicted in FIGS. 3 and4, other frequency multipliers and dividers may be used in accord withthe present invention.

From the foregoing description, it will be apparent that the presentinvention has a number of advantages, some of which have been describedherein, and others of which are inherent in the embodiments of theinvention described herein. Also, it will be understood thatmodifications can be made to the apparatus and method for frequencyup-conversion and down conversion described herein without departingfrom the teachings of the subject matter described herein. As such, theinvention is not to be limited by the described embodiments except asrequired by the appended claims.

1. An apparatus for bi-directional frequency conversion comprising: a first 180 degree coupler having a first coupler port A receiving a signal at a first frequency, a first coupler port B, a first coupler port C, and a first coupler port D outputting a signal at the first frequency; a second 180 degree coupler having a second coupler port A, a second coupler port B receiving a signal at a second frequency, a second coupler port C outputting a signal at the second frequency, and a second coupler port D; and two frequency multiplier circuits, wherein one of the two frequency multiplier circuits being coupled between first coupler port B and second coupler port A and the other of the two frequency multiplier circuits being coupled between first coupler port C and second coupler port D.
 2. The apparatus of claim 1 wherein at least one of the frequency multiplier circuits is a bi-directional diode-based passive frequency multiplier circuit.
 3. The apparatus of claim 2, wherein the bi-directional diode-based passive frequency multiplier circuit comprises a heterojunction barrier varactor diode.
 4. The apparatus of claim 2, wherein the bi-directional diode-based passive frequency multiplier circuit comprises: a diode having a first terminal and a second terminal; a first filter circuit coupled to the first terminal of the diode, the first filter circuit configured to present an open circuit at the first frequency and a short circuit at the second frequency, wherein the second frequency is an odd harmonic of the first frequency; and a second filter circuit coupled to the second terminal of the diode, the second filter circuit configured to present a short circuit at the first frequency and an open circuit at the second frequency.
 5. The apparatus of claim 2, wherein the diode-based passive frequency multiplier circuit comprises: a diode configured as a shunt diode, the shunt diode having a common terminal; a first filter circuit coupled to the common terminal of the diode, the first filter circuit configured to present a short circuit at the first frequency and an open circuit at the second frequency, wherein the second frequency is an odd harmonic of the first frequency; and a second filter circuit coupled to the common port of the diode, the second filter circuit configured to present an open circuit at the first frequency and a short circuit at the second frequency.
 6. The apparatus of claim 1, wherein the frequency multiplier circuits comprise passive frequency tripler circuits.
 7. An apparatus for up converting a first signal at a first frequency to a second frequency and for down converting a second signal at the second frequency to the first frequency, the apparatus comprising: first means for asymmetric coupling, the first means having a first means input port, a first means output port, a first means first bi-directional port, and a first means second bi-directional port, and wherein the first signal is coupled to the first means input port; second means for asymmetric coupling, the second means having a second means input port, a second means output port, a second means first bi-directional port, and a second means second bi-directional port, and wherein the second signal is coupled to the second means input port; first means for frequency multiplying and frequency dividing, the first means for frequency multiplying and frequency dividing coupled to the first means first bi-directional port and to the second means first bi-directional port; and second means for frequency multiplying and frequency dividing, the second means for frequency multiplying and frequency dividing coupled to the first means second bi-directional port and the second means second bi-directional port.
 8. The apparatus according to claim 7, wherein the first means for asymmetric coupling or the second means for asymmetric coupling comprises a 180 degree hybrid coupler or the first means for asymmetric coupling and the second means for asymmetric coupling both comprise 180 degree hybrid couplers.
 9. The apparatus according to claim 7, wherein the first means for frequency multiplying and frequency dividing or the second means for frequency multiplying and frequency dividing comprises a frequency multiplier circuit or the first means for frequency multiplying and frequency dividing and the second means for frequency multiplying and frequency dividing both comprise frequency multiplier circuits.
 10. The apparatus of claim 9 wherein at least one of the frequency multiplier circuits is a bi-directional diode-based passive frequency multiplier circuit.
 11. The apparatus of claim 10, wherein the bi-directional diode-based passive frequency multiplier circuit comprises a heterojunction barrier varactor diode.
 12. The apparatus of claim 10, wherein the bi-directional diode-based passive frequency multiplier circuit comprises: a diode having a first terminal and a second terminal; a first filter circuit coupled to the first terminal of the diode, the first filter circuit configured to present an open circuit at the first frequency and a short circuit at the second frequency, wherein the second frequency is an odd harmonic of the first frequency; and a second filter circuit coupled to the second terminal of the diode, the second filter circuit configured to present a short circuit at the first frequency and an open circuit at the second frequency.
 13. The apparatus of claim 10, wherein the bi-directional diode-based passive frequency multiplier circuit comprises: a diode configured as a shunt diode, the shunt diode having a common terminal; a first filter circuit coupled to the common terminal of the diode, the first filter circuit configured to present a short circuit at the first frequency and an open circuit at the second frequency, wherein the second frequency is an odd harmonic of the first frequency; and a second filter circuit coupled to the common terminal of the diode, the second filter circuit configured to present an open circuit at the first frequency and a short circuit at the second frequency.
 14. The apparatus of claim 9, wherein the frequency multiplier circuits comprise passive frequency tripler circuits.
 15. A transceiver comprising: a transceiver element having a transmit port providing a transmit signal at a first frequency and a receive port adapted to receive a receive signal at said first frequency; a radiating element; a receiving element; a first 180 degree coupler having a first coupler port A coupled to the transmit port, a first coupler port B, a first coupler port C, and a first coupler port D coupled to the receive port, wherein the first coupler port A is configured to receive a signal at a first frequency and the first coupler port D is configured to output a signal at the first frequency; a second 180 degree coupler having a second coupler port A, a second coupler port B coupled to the receiving element, a second coupler port C coupled to the radiating element, and a second coupler port D, wherein the second coupler port B is configured to receive a signal at a second frequency and the second coupler port C is configured to output a signal at the second frequency, wherein the second frequency is higher than the first frequency; and two frequency multiplier circuits, wherein one of the two frequency multiplier circuits is coupled to the first coupler port B and to the second coupler port A or the second coupler port D and the other of the two frequency multiplier circuits is coupled to the first coupler port C and to the second coupler port A or the second coupler port D.
 16. The transceiver according to claim 15 wherein at least one of the frequency multiplier circuits is a bi-directional diode-based passive frequency multiplier circuit.
 17. The transceiver according to claim 16, wherein the bi-directional diode-based passive frequency multiplier circuit comprises a heterojunction barrier varactor diode.
 18. The transceiver according to claim 16, wherein the bi-directional diode-based passive frequency multiplier circuit comprises: a diode having a first terminal and a second terminal; a first filter circuit coupled to the first terminal of the diode, the first filter circuit configured to present an open circuit at the first frequency and a short circuit at the second frequency, wherein the second frequency is an odd harmonic of the first frequency; and a second filter circuit coupled to the second terminal of the diode, the second filter circuit configured to present a short circuit at the first frequency and an open circuit at the second frequency.
 19. The transceiver according to claim 16, wherein the diode-based passive frequency multiplier circuit comprises: a diode configured as a shunt diode, the shunt diode having a common terminal; a first filter circuit coupled to the common terminal of the diode, the first filter circuit configured to present a short circuit at the first frequency and an open circuit at the second frequency, wherein the second frequency is an odd harmonic of the first frequency; and a second filter circuit coupled to the common terminal of the diode, the second filter circuit configured to present an open circuit at the first frequency and a short circuit at the second frequency.
 20. The transceiver according to claim 16, wherein the frequency multiplier circuits comprise passive frequency tripler circuits.
 21. An apparatus comprising: means for transceiving, said means producing a transmit signal at a first frequency at a transmit port and receiving a receive signal at the first frequency at a receive port; means for radiating a signal at a second frequency; means for receiving a radiated signal at the second frequency; first means for asymmetric coupling, the first means having a first means input port coupled to the transmit port, a first means output port coupled to the receive port, a first means first bi-directional port, and a first means second bi-directional port; second means for asymmetric coupling, the second means having a second means input port coupled to the means for receiving, a second means output port coupled to the means for radiating, a second means first bi-directional port, and a second means second bi-directional port; first means for frequency multiplying and frequency dividing, the first means for frequency multiplying and frequency dividing coupled to the first means first bi-directional port and to the second means first bi-directional port; and second means for frequency multiplying and frequency dividing, the second means for frequency multiplying and frequency dividing coupled to the first means second bi-directional port and the second means second bi-directional port.
 22. The apparatus according to claim 21, wherein the first means for coupling or the second means for coupling comprises a 180 degree hybrid coupler or the first means for coupling and the second means for coupling both comprise 180 degree hybrid couplers.
 23. The apparatus according to claim 21, wherein the first means for frequency multiplying and frequency dividing or the second means for frequency multiplying and frequency dividing comprises a frequency multiplier circuit or the first means for frequency multiplying and frequency dividing and the second means for frequency multiplying and frequency dividing both comprise frequency multiplier circuits.
 24. The apparatus of claim 23 wherein at least one of the frequency multiplier circuits is a bi-directional diode-based passive frequency multiplier circuit.
 25. The apparatus of claim 24, wherein the bi-directional diode-based passive frequency multiplier circuit comprises a heterojunction barrier varactor diode.
 26. The apparatus of claim 24, wherein the bi-directional diode-based passive frequency multiplier circuit comprises: a diode having a first terminal and a second terminal; a first filter circuit coupled to the first terminal of the diode, the first filter circuit configured to present an open circuit at the first frequency and a short circuit at the second frequency, wherein the second frequency is an odd harmonic of the first frequency; and a second filter circuit coupled to the second terminal of the diode, the second filter circuit configured to present a short circuit at the first frequency and an open circuit at the second frequency.
 27. The apparatus of claim 24, wherein the bi-directional diode-based passive frequency multiplier circuit comprises: a diode configured as a shunt diode, the shunt diode having a common terminal; a first filter circuit coupled to the common terminal of the diode, the first filter circuit configured to present a short circuit at the first frequency and an open circuit at the second frequency, wherein the second frequency is an odd harmonic of the first frequency; and a second filter circuit coupled to the common terminal of the diode, the second filter circuit configured to present an open circuit at the first frequency and a short circuit at the second frequency.
 28. The apparatus of claim 23, wherein the frequency multiplier circuits comprise passive frequency tripler circuits. 